The present invention relates to the parenteral administration, by injection, of medicamental or other formulations which are neither liquids, like the conventional injectable formulations, nor solids, like implants, but are pasty or very viscous and are referred to below as semi-solid formulations.
There are many alternative forms of syringes for the parenteral injection of liquids by means of a needle for parenteral injection. These syringes are practically unusable for the parenteral administration of semi-solid formulations.
Various devices for the parenteral administration of solid formulations, such as implants, are also known, these using trocars of relatively large diameter and being combined with expulsion means allowing the formulation to be expelled from the trocar, for example by withdrawing the latter. Other administration means use catheters.
Also known are syringes intended for the administration of pasty products in dentistry, which allow cements or other materials to be deposited in dental cavities. Examples of such syringes are described in U.S. Pat. Nos. 4,121,587 and 5,603,701 which provide a syringe body in which a piston moves in order to expel the pasty mass through a needle, using means for moving the piston which are based on a threaded rod passing through a complementary immobile thread, in order to gear down the force necessary to expel the pasty mass. However, these syringes are not capable of suitable parenteral injection and are very complex, whether they be specially designed in all their parts or have elements designed to be used with conventional syringe bodies, which means that they are ill-suited to multiple use and are especially in the form of a disposable or non-reusable syringe or carpule.